A standard transfer apparatus of the above-described type is typically used to load a group containing a predetermined number of bottles or other objects onto a pallet or case. An input conveyor brings the bottles into a pickup station where they are grouped in a dense array, each bottle assuming a predetermined position. Then the transfer device picks up all the bottles and moves them in a horizontal transport direction to a deposition station where they are set down, for instance positioned in the pockets of a group of six-pack containers themselves sitting a cardboard case.
Such an apparatus must be perfectly vertically aligned with the objects as they are being picked up and with the pallet or case into which they are being set. At the same time it must be able to move fairly rapidly to keep up with the upstream and downstream equipment.
While the obvious way to ensure such accurate positioning is to provide a rigid guide framework on which the lift plate can move vertically, such a solution is clearly not advisable because the extra mass is difficult to start, stop, and move rapidly. Thus recourse is made to solutions which provide the desired accurate positioning while being less massive.
In one known solution the lift plate, which typically has a plurality of suction grabs or grab bars for lifting the bottles or other objects, is carried at the lower end of four wide belts that are wound up on respective rollers on the outer end of a horizontally movable arm or carriage. The roller axes form a rectangle and the rollers are connected to each other for synchronous operation by right-angle drives so all of the belts are payed out and wound up at the same speed. Since each such wide belt is relatively stiff parallel to its plane, the result is that the lift plate remains fairly accurately positioned underneath the carriage. The considerable disadvantage of this solution is that the belts completely contain all the structure between the top of the lift plate and the bottom of the carriage, making servicing this equipment extremely difficult.
In another known solution the lift plate is carried on parallelogrammatic linkages whose links are connected together by sector gears so that they all extend and retract synchronously. Such an arrangement works fairly well, but is prone to considerable wear due to its complex mechanics. Once the sector gears and bearings start to wear, action becomes sloppy and the lift plate's position shifts relative to the overlying structure.